Not Applicable.
Not Applicable.
Nozzle jets have been used for several years in rotary cone rock bits both in or near the center of the rock bit and around the peripheral edge of the bit to encourage cone cleaning, to enhance removal of debris from a borehole bottom, and to efficiently cool the face of the rock bit.
Rotary cone rock bits are typically configured with multiple jet nozzle exits spaced at regular intervals along the periphery of the bit. High velocity fluid from these jet nozzles impacts the hole bottom and removes rock cuttings and debris. Center jets are also used in rotary cone rock bits for a variety of reasons. These include enhanced cone cleaning, protection against bit balling, and increased total flow of drilling fluid through the drill bit without creating washout problems.
Too much drilling fluid exiting the peripheral jets is believed to encourage undesirable re-circulation paths for drilling fluid at the bottom of the wellbore. In fact, all else being equal, it is thought desirable to have all or nearly all the drilling fluid exit the center jet. However, due to erosion concerns typically only 15 to 30 percent of the total hydraulic fluid (drilling fluid or drilling mud) flow passes through the center jet, with the remainder of the mud being jetted through the peripheral nozzles. In particular, excessive drilling fluid flow through the center jet causes flow erosion at the cutter surfaces, resulting in premature failure of the rock bit. Even when fluid flow through the peripheral jets might be desirable, such as for cleaning the cutting teeth on the roller cones in sticky formations, excessive erosion of the cone shell and other components is a concern.
Many techniques have been used in an effort to optimize the bit hydraulics by modifying the nozzle configuration on the peripheral jets by moving the nozzle closer to the hole bottom, changing the nozzle jet vector, or both. U.S. Pat. Nos. 4,687,067; 4,784,231; 4,239,087; 3,070,182; 4,759,415; 5,029,656; and 5,495,903 teach modifications to the peripheral jets to improve the bit hydraulics, and each is hereby incorporated by reference for all purposes.
Three different types of nozzles are commonly used in center jet applications i.e. the diverging diffuser nozzle, the standard, non-diverging nozzle and the mini-extended nozzle. A less commonly utilized center jet nozzle has multiple discharge ports. Multiple exit nozzles are desirable since they offer the most flexibility to the designer to orient the flow patterns to clean the cutters or to improve borehole cleaning. However, multiple exit nozzles have two major design problems. First, the size for each of the exit ports is necessarily small because the total flow area (TFA) of a multiple exit nozzle is equal to the sum of the exit areas and to keep the total flow to within tolerable limits, the individual exit nozzles are necessarily small. As a result, the jet nozzle is prone to plugging. Second, the small nozzle size does nothing to reduce the exit flow velocity. Even though the flow is redirected, high fluid flow rates through each nozzle pointed toward metal components will likely lead to surface erosion and possible catastrophic failure.
A drill bit is needed that provides more efficient drilling fluid flow from the bottom of the borehole without increased erosion concerns around the drill bit. Ideally, this could be accomplished by a novel jet nozzle design or combination, so that the basic drill bit design would remain unchanged.
A disclosed embodiment of the invention is a drill bit with one or more attached multi-stage diffuser nozzles. The nozzles of this embodiment include a flow restrictor component distinct from a fluidic distributor component, allowing the selective matching of different sized or shaped flow restrictors and fluidic distributors. The flow restrictor has an internal passage to carry fluid from the liquid plenum of the drill bit, the internal passage including a throat of effective cross-sectional area A0E. The fluid distributor, downstream from the flow restrictor, includes a fluid exit region with an effective cross-sectional area A1E greater than A0E.
This embodiment of the invention may also include numerous variations. For example, the fluidic distributor may be designed to project drilling fluid toward the hole bottom at a variety of desired angles. To minimize undesired pressure fluctuations in the drilling fluid, a transition region of effective cross-sectional area A2 may be added, either as a distinct component or not. Effective cross-sectional area A2 would therefore be larger than either A0E or A1E. The drill bit may also be designed so that the diffuser nozzle is either closer to the longitudinal axis of the bit or the periphery of the bit.
A second embodiment of the invention is a nozzle body which may be manufactured from only a single component. This nozzle body includes a first set of one or more passages at an upper end that, combined, are a first cross-sectional area. It also includes a second set of one or more passages at a lower end that, combined, are a second cross-sectional area, the second cross-sectional area being greater than the first cross-sectional area. In addition, the second set of passages directs at least a portion of the fluid along a vector that is not collinear with the central axis of the nozzle body. Similar to the first embodiment, this embodiment may advantageously include a transition region between the first and second sets of passages, the transition region having a cross-sectional area that is greater than either of the first or second cross-sectional areas. The first and second sets of passages may have a variety of configurations. For example, their cross-sectional areas may vary along their lengths, they may be circular or non-circular, they may direct drilling fluid from exit ports in the fluidic distributor at a variety of angles, they may be straight or curved, etc.
A third embodiment of the invention may be expressed as a method of controlling fluid flow through a drill bit. This method includes lowering the fluid pressure of drilling fluid flowing through a drill bit from an initial pressure (such as that present inside the fluid plenum) to a choke pressure, dampening the fluid pressure oscillations in the drilling fluid, and increasing the fluid pressure to an exit pressure (such as that present in the annulus of the wellbore). The exit pressure is necessarily higher than the choke pressure in this embodiment. The drilling fluid pressure may be lowered to the choke pressure by a first single passage, for example. The drilling fluid pressure may then be raised to the transition pressure by a second passage having a cross-sectional area greater than that of the first single passage. One implementation of this embodiment ensures that the difference between the initial pressure and the transition pressure is greater than the difference of the transition pressure and the exit pressure.
The various characteristics described above, as well as other features, will be readily apparent to those skilled in the art upon reading the following detailed description of the preferred embodiments of the invention, and by referring to the accompanying drawings.